Study On Space Charge Characteristics And Dielectric Properties Of LDPE Containing Micro-and Nano-sized SiO₂ Particles

Insulation materials are the basis of electrical insulation.Polymer materials are widely used in electrical insulation because of its good electrical insulation performance and processability,and the heat resistance cannot be ignored in electrical equipment with high insulation level.Research shows that adding micron particles to the polymer can increase the thermal conductivity of the composite,but it will decrease the electrical insulation performance at the same time.Therefore,in this paper,microparticles and nanoparticles are added to the polymer,and the effects of microparticles and nanoparticles on the electrical insulation properties of polymer composites are investigated.In this paper,the LDPE is used as tmatrix polymer,micro-SiO₂ and nano-SiO₂ are used as filler,the micro-nano-composites with different contents of micro-SiO₂ and nano-SiO₂ is prepared by the method of melt blending.SEM,FTIR and DSC were used to characterize the structures of micro-nano-composites.The method of pulse electro-acoustic is used to measure the space charge of micro-nano-composites.The conductivity current,dielectric strength,relative permittivity and loss factor of the micro-nano-composites are tested.The experimental results show that nano-SiO₂ can form stronger bonding with LDPE matrix than micro-SiO₂,and the crystallinity of nanocomposites is higher than micro-composites,the crystallinity of micro-nano-composites is between nanocomposites and micro-composites.The addition of nano-SiO2 or micro-SiO2 can reduce the conductance current of the composites,and increase the electric charge injection threshold electric field,thereby reducing the charge accumulation.When the nano-SiO2 content is 0.5wt%,the conductance current of the composite is minimum,the inhibition effect on charge accumulation is the best.And because of the coexistence of two kinds of fillers in micro-nano-composites,the inhibition effect on space charge is between nanocomposites and micro-composites.The DC breakdown strength and the AC breakdown strength of nanocomposites are higher than pure polyethylene and decrease with the increase of the content of nano filler.The DC breakdown strength of micro-composites is lower than pure polyethylene,while the AC breakdown strength is higher than pure polyethylene.The DC breakdown strength of micro-nano-composite is between nanocomposites and micro-composites and there is little change with the nano-filler content increasing,but the AC breakdown strength is higher than micro-composites and increase with the nano-filler content increasing.The relative dielectric constant and dielectric loss factor of the composites are all higher than pure LDPE and in proportion to the content of the fillers.And the relative dielectric constant decreases with the increase of temperature and electric field frequency,the dielectric loss factor decreases with the increase of the electric field frequency,and increases with the increase of the temperature.